Polyamide resins are widely used as engineering plastics having excellent mechanical strength such as impact resistance and friction/abrasion resistance as well as excellent heat resistance and oil resistance in the fields of automotive parts, electronic/electric equipment parts, office automation equipment parts, machine parts, construction materials/housing parts and the like, and recently have found increasingly wide applications.
Many classes of polyamide resins including e.g., polyamide 6 and polyamide 66 are known, among which m-xylylene adipamide (hereinafter sometimes referred to as “MXD6”) derived from m-xylylenediamine and adipic acid is positioned as a very excellent polyamide resin because it contains an aromatic ring in the main chain unlike polyamide 6 and polyamide 66 so that it has high rigidity, low water absorption and excellent oil resistance as well as a low shrinkage ratio during molding and causes little shrinkage or warp, which means that it is also suitable for precision molding. Thus, MXD6 has recently been more widely used as a molding material, especially extrusion molding material in various fields including electronic/electric equipment parts, parts of vehicles such as automobiles, general machine parts, precision machine parts, leisure/sports goods, civil engineering and construction materials, etc.
On the other hand, there have recently been increasingly growing commercial needs in applications requiring high heat resistance, such as reflectors in LED illumination and LED mounting boards, which require high heat resistance during manufacturing or use thereof.
Patent documents 1 to 4 propose to use various polyamide resin compositions for these applications. Patent document 1 discloses a composition comprising a semiaromatic polyamide composed of terephthalic acid and 1,9-nonanediamine and 2-methyl-1,8-octanediamine in combination with titanium oxide, magnesium hydroxide and a filler. This polyamide shows a high melting point around 306° C., for example, but undesirably has problems such as difficulty in molding and low productivity because of poor melt flowability, susceptibility of the resin to decomposition and high gas emission and the like.
In such applications requiring high heat resistance, polyamide resins having a melting point of 280° C. or more, especially higher than 300° C. are desired, but polyamide resins having not only such a high melting point but also excellent moldability have not actually reached an industrially satisfactory level at present.